Method and apparatus for charging multiple energy storage devices

ABSTRACT

An electric vehicle includes a controller configured to receive sensor feedback from a high voltage storage device and from a low voltage storage device, compare the sensor feedback to operating limits of the respective high and low voltage storage device, determine, based on the comparison a total charging current to the high voltage storage device and to the low voltage storage device and a power split factor of the total charging current to the high voltage device and to the low voltage device, and regulate the total power to the low voltage storage device and the high voltage storage device based on the determination.

CROSS REFERENCE TO RELATED APPLICATION

The present invention is a continuation of and claims priority to U.S.patent application Ser. No. 13/476,165, filed May 21, 2012, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to electric drive systemsincluding hybrid and electric vehicles and, more particularly, tocharging energy storage devices of an electric vehicle using a multiportenergy management system.

Hybrid electric vehicles may combine an internal combustion engine andan electric motor powered by an energy storage device, such as atraction battery, to propel the vehicle. Such a combination may increaseoverall fuel efficiency by enabling the combustion engine and theelectric motor to each operate in respective ranges of increasedefficiency. Electric motors, for example, may be efficient ataccelerating from a standing start, while internal combustion engines(ICEs) may be efficient during sustained periods of constant engineoperation, such as in highway driving. Having an electric motor to boostinitial acceleration allows combustion engines in hybrid vehicles to besmaller and more fuel efficient.

Purely electric vehicles use stored electrical energy to power anelectric motor, which propels the vehicle and may also operate auxiliarydrives. Purely electric vehicles may use one or more sources of storedelectrical energy. For example, a first source of stored electricalenergy may be used to provide longer-lasting energy, such as alow-voltage battery (commonly referred to as an ‘energy battery’) whilea second source of stored electrical energy may be used to providehigher-power energy for, for example, vehicle acceleration, using ahigh-voltage battery (commonly referred to as a ‘power battery’). Knownenergy storage devices may also include an ultracapacitor, which tendsto have fast charging and discharging capability and provides long lifeoperation.

Plug-in electric vehicles, whether of the hybrid electric type or of thepurely electric type, are typically configured to use electrical energyfrom an external source to recharge the energy storage devices. Suchvehicles may include on-road and off-road vehicles, golf carts,neighborhood electric vehicles, forklifts, and utility trucks asexamples. Known charging devices include a multiport energy storagemanagement system (ESMS) for charging both low voltage and high voltageenergy storage systems of an electric vehicle. Typically, an ESMSincludes buck-boost converters which can be used in conjunction with oneanother in order to flexibly apply charging voltages to a variety ofdevices having different charging voltage requirements. An ESMS alsotypically includes a high voltage side and a low voltage side. In oneknown ESMS device having four ports, two of the ports are on a highvoltage side of the device and two of the ports are on a low voltageside of the device. The high voltage side is typically used for chargingfrom a utility grid or renewable energy source (one port on the highvoltage side) and for providing charging power to a power battery(another port on the high voltage side). The low voltage side istypically used for charging low voltage devices such as energy batteriesand ultracapacitors of the electric vehicle (ports on the low voltageside) and may, in some embodiments, also include adaptability to a lowvoltage charging source as well, in one of the low voltage ports.

A power battery, incidentally, is typically included in order to providehigh power bursts for acceleration of the vehicle, as opposed to anenergy battery, which is typically included in order to providelong-range cruising energy to the vehicle and it is therefore desirableto operate as a high voltage device. Thus, because of the high powerrequirements of the power battery, high voltage energy storage devicessuch as power batteries typically operate under a high voltage operationof 400 V or more, while low voltage energy storage devices such asenergy batteries typically provide high energy storage and operate at amuch lower nominal voltage, such as 120 V or below. Ultracapacitors canbe used in either high or low voltage applications and thus can beincluded on either the high side or the low side of the ESMS chargingdevice, depending on their type of use (high bursts of power vs. energystorage for cruising).

Because of the buck-boost converters in the ESMS, multiple arrangementsof energy storage devices and power sources may be utilized in order tocharge the energy storage devices. That is, a known ESMS is flexiblyconfigurable in that a charging voltage may be first bucked down, andthen boosted up to a desired charging voltage on the high voltage side.And, because of the bucking and subsequent boosting operations, thecharging on the high side may be either above or below the chargingvoltage provided externally. Similarly, the charging voltage may bebucked to the lower voltage of the low voltage side as well. Further,because of the multiple buck-boost converters in an EMS, the chargingvoltage may be simultaneously provided to charge both the high voltagedevice on the high side, as well as one or more low voltage devices onthe low side. That is, a single high voltage supply may be split tosimultaneously provide energy to the high side and the low side devices,or to two low side devices, as examples.

Known devices that split power for charging multiple energy storagedevices are typically optimized based simply on a condition of thedevices that are being charged. That is, known charging or ESMS devicestypically base their power split on factors such as the state-of-chargeof the device(s) and/or the voltage at each respective charging port.Although such an optimization often can be adequate to provide a maximumoverall rate of charging to the combination of devices being charged,such a charging scheme does not take into account additional factorssuch as the overall implications to the life of the devices themselvesthat are being charged, their temperature limits, and the like. That is,although energy storage devices may be physically capable of receiving ahigh rate of charge in order to minimize charging time of all devices,it may not be desirable to do so if the long-term cost to one or more ofthe devices is a drop in life.

In other words, the lifecycle cost and eventual need to replace storagedevices such as power batteries, energy batteries, and ultracapacitorsmay not be worth the marginal decrease in charging time when charging isbased on a state-of-charge alone. In fact, because known chargingdevices determine power splits and charging rates without taking intoaccount the specifics of the devices themselves (but rather are simplybased on a state-of-charge or a voltage at the charging terminals), thedevices not only have a longtime risk of life, but are also at risk ofcatastrophic failure if charged beyond a rate than the device canhandle.

It would therefore be desirable to provide an apparatus and controlscheme to optimize overall recharge time for multiple energy storagedevices of an EV while taking into account the life implications of thecharging scheme.

BRIEF DESCRIPTION OF THE INVENTION

The invention is a method and apparatus for optimizing a total rechargetime for multiple energy storage devices of an EV, accounting for lifeimplications to the energy storage devices themselves.

According to one aspect of the invention, an electric vehicle includes acontroller configured to receive sensor feedback from a high voltagestorage device and from a low voltage storage device, compare the sensorfeedback to operating limits of the respective high and low voltagestorage device, determine, based on the comparison a total chargingcurrent to the high voltage storage device and to the low voltagestorage device and a power split factor of the total charging current tothe high voltage device and to the low voltage device, and regulate thetotal power to the low voltage storage device and the high voltagestorage device based on the determination.

In accordance with another aspect of the invention, a method of managingan energy storage system for an electric vehicle includes receivingsensor feedback from a high voltage energy storage device of theelectric vehicle, comparing the sensor feedback from the high voltageenergy storage device to an operating limit specific to the high voltageenergy storage device, receiving sensor feedback from a low voltageenergy storage device of the electrical vehicle, comparing the sensorfeedback from the low voltage energy storage device to an operatinglimit specific to the low voltage energy storage device, determining,based on the comparison from the high voltage device and from the lowvoltage device a total charging current to the high voltage storagedevice and to the low voltage storage device and a power split factor ofthe total charging current to the high voltage device and to the lowvoltage device, and regulating the total power to the low voltagestorage device and the high voltage storage device based on thedetermination.

In accordance with yet another aspect of the invention, a computerreadable storage medium coupled to an energy storage and managementsystem (ESMS) of an electric vehicle (EV) and having stored thereon acomputer program comprising instructions which when executed by acomputer cause the computer to receive sensor feedback from a highvoltage energy storage device of the EV and from a low voltage energystorage device of the EV, compare the sensor feedback to operatinglimits of the respective energy storage devices, determine, based on thecomparison a total charging current to the energy storage devices and apower split factor of the total charging current between the highvoltage device and the low voltage device, and regulate the total powerto the energy storage devices based on the determination.

Various other features and advantages will be made apparent from thefollowing detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a schematic block diagram of an electric vehicle (EV)incorporating embodiments of the invention.

FIG. 2 is a schematic diagram of a configurable multi-port chargerarchitecture according to an embodiment of the invention.

FIG. 3 illustrates an electrical schematic of a multi-port chargeraccording to an embodiment of the invention.

FIG. 4 illustrates a control scheme, as an example, specific to moduleM2 of FIG. 2.

FIGS. 5 and 6 illustrate flow of a charging current in a multi-portcharger in exemplary modes of operation.

FIG. 7 is a table illustrating configurations as of the multi-portcharger illustrated in FIG. 2.

FIG. 8 is a block diagram illustrating a recharging scenario and use ofa communication interface, according to an embodiment of the invention.

FIG. 9 illustrates control variables and parameters with respect to acommunication interface, according to an embodiment of the invention.

FIG. 10 is a schematic block diagram of an electric vehicle (EV) havingan auxiliary power unit (APU) incorporating embodiments of theinvention.

FIG. 11 is a schematic block diagram of an electric vehicle (EV) havingan auxiliary power unit (APU) incorporating embodiments of theinvention.

DETAILED DESCRIPTION

FIG. 1 illustrates one embodiment of a hybrid electric vehicle (HEV) orelectric vehicle (EV) 10, such as an automobile, truck, bus, or off-roadvehicle, for example, incorporating embodiments of the invention. Inother embodiments vehicle 10 includes one of a vehicle drivetrain, anuninterrupted power supply, a mining vehicle drivetrain, a miningapparatus, a marine system, and an aviation system. Vehicle 10 includesan energy storage and management system (ESMS) 100 that is controlled bya controller or computer 46, an internal combustion or heat engine 12, atransmission 14 coupled to engine 12, a differential 16, and a driveshaft assembly 18 coupled between transmission 14 and differential 16.And, although ESMS 100 is illustrated in a plug-in hybrid electricvehicle (PHEV), it is understood that ESMS 100 is applicable to anyelectric vehicle, such as a HEV or EV or other power electronic drivesused to operate pulsed loads, according to embodiments of the invention.

According to various embodiments, engine 12 may be an internalcombustion gasoline engine, an internal combustion diesel engine, anexternal combustion engine, or a gas turbine engine, as examples. System10 includes an engine controller 20 provided to control operation ofengine 12. According to one embodiment, engine controller 20 includesone or more sensors 22 that are configured to sense operating conditionsof engine 12. Sensors 22 may include an rpm sensor, a torque sensor, anoxygen sensor, and a temperature sensor, as examples. As such, enginecontroller 20 is configured to transmit or receive data from engine 12.Vehicle 10 also includes an engine speed sensor (not shown) thatmeasures a crankshaft speed of engine 12. According to one embodiment,speed sensor may measure engine crankshaft speed from a tachometer (notshown) in pulses per second, which may be converted to a revolutions perminute (rpm) signal.

Vehicle 10 also includes at least two wheels 24 that are coupled torespective ends of differential 16. In one embodiment, vehicle 10 isconfigured as a rear wheel drive vehicle such that differential 16 ispositioned near an aft end of vehicle 10 and is configured to drive atleast one of the wheels 24. Optionally, vehicle 10 may be configured asa front-wheel drive vehicle. In one embodiment, transmission 14 is amanually operated transmission that includes a plurality of gears suchthat the input torque received from engine 12 is multiplied via aplurality of gear ratios and transmitted to differential 16 throughdrive shaft assembly 18. According to such an embodiment, vehicle 10includes a clutch (not shown) configured to selectively connect anddisconnect engine 12 and transmission 14.

Vehicle 10 also includes an electromechanical device such as an electricmotor or electric motor/generator unit 26 coupled along drive shaftassembly 18 between transmission 14 and differential 16 such that torquegenerated by engine 12 is transmitted through transmission 14 andthrough electric motor or electric motor/generator unit 26 todifferential 16. A speed sensor (not shown) may be included to monitoran operating speed of electric motor 26. According to one embodiment,electric motor 26 is directly coupled to transmission 14, and driveshaft assembly 18 comprises one axle or drive shaft coupled todifferential 16.

A hybrid drive control system or torque controller 28 is provided tocontrol operation of electric motor 26 and is coupled to motor/generatorunit 26. An energy storage system 30 is coupled to torque controller 28and is controllable by ESMS 100. Energy storage system 30 comprises alow voltage energy storage or energy battery 32, a high voltage energystorage or power battery 34, and an ultracapacitor 36, as examples.However, although a low voltage energy storage 32, a high voltage energystorage 34, and an ultracapacitor 36 are illustrated, it is to beunderstood that energy storage system 30 may include a plurality ofenergy storage units as understood in the art such as sodium metalhalide batteries, sodium nickel chloride batteries, sodium sulfurbatteries, nickel metal hydride batteries, lithium ion batteries,lithium polymer batteries, nickel cadmium batteries, a plurality ofultracapacitor cells, a combination of ultracapacitors and batteries, ora fuel cell, as examples. An accelerator pedal 38 and brake pedal 40 arealso included in vehicle 10. Accelerator pedal 38 is configured to sendthrottle command signals or accelerator pedal signals to enginecontroller 20 and torque control 28.

System 10 includes a charger interface 42 coupled to energy storageunits 32-36 of energy storage system 30 via ESMS100, according toembodiments of the invention. Charger interface 42 may be coupled tomultiple energy storage systems 32-36, as illustrated and chargerinterface 42 may be coupled to one or multiple power input lines 44, twoof which are illustrated, according to embodiments of the invention.ESMS 100 is configured to selectively engage and disengage DC electricaldevices or buck-boost modules as will be discussed. In one embodimentand as will be illustrated, charger interface 42 is connectable to ahigh voltage port of ESMS 100. Typically, charger interface 42 includesan interface to the one or more input lines 44 such that power frominput lines is connectable to a charging port of ESMS 100.

Although charger interface 42 is illustrated as being coupled to energystorage systems 32-36 via ESMS 100, and charger interface 42 isillustrated as coupled to one or multiple power input lines 44, it is tobe understood that embodiments of the invention are not to be solimited. Instead, it is to be understood that charger interface 42 maybe coupled to multiple and varying types of energy storage systems andpower inputs. Further, there may be multiple charger interfaces 42 orESMS units 100 per vehicle, or that there may be power systems appliedto each wheel 24 of vehicle 10, each having a charger interface 42coupled thereto.

In operation, it is understood in the art that energy may be provided todrive shaft assembly 18 from internal combustion or heat engine 12 viatransmission 14, and energy may be provided to drive shaft assembly 18via drive control system 28 having energy drawn from energy storagesystem 30 that may include energy systems 32-36. Thus, as understood inthe art, energy may be drawn for vehicle 10 boost or acceleration from,for instance a high voltage storage device 34 that may include abattery, as an example, or from ultracapacitor 36. During cruising(i.e., generally non-accelerating operation), energy may be drawn forvehicle 10 via a low voltage storage device such as low voltage energystorage 32.

And, during operation, energy may be drawn from internal combustion orheat engine 12 in order to provide energy to energy storage 30, orprovide power to drive shaft assembly 18 as understood in the art.Further, some systems include a regenerative operation where energy maybe recovered from a braking operation and used to re-charge energystorage 30. In addition, some systems may not provide regenerativeenergy recovery from braking and some systems may not provide a heatengine such as internal combustion or heat engine 12. Nevertheless anddespite the ability of some systems to re-charge energy storage 30,energy storage 30 periodically requires re-charging from an externalsource such as a 115 V household supply or a 230 V 3-phase source, asexamples. The requirement to re-charge energy storage 30 is particularlyacute in a plug-in hybrid electric vehicle (PHEV) having no heat engineto provide power and an extended range of driving operation.

Thus, embodiments of the invention are flexible and configurable havinga plurality of energy ports, and may be coupled to multiple powersources and source types in order to charge one or multiple energystorage types. Further, embodiments of the invention allow efficient andbalanced charging of multiple energy systems 32-36 of energy storageunit 30, the multiple energy systems having varying levels of depletion.

To meet the demands of modern PHEVs and EVs, the infrastructure shouldprovide typically 7 kW to achieve a state-of-charge (SOC) gain of 80%(assuming a 25 kWh battery) in a charging time of 2 or 3 hours (homecharging). For a more aggressive short stop fast charging scenario(e.g., a “gas station”) significant higher power levels may be requiredto achieve a desired 80% SOC in 10 minutes. The vehicle interface needsto be designed according to existing standards. A pilot signaldetermines by its duty cycle the maximum allowable power. Besides a highdegree of integration the proposed system provides also single and orthree phase AC input, high efficiency, low harmonics, nearly unity inputpower factor, low cost, low weight and safety interlocking of theequipment. The power factor correction (PFC) requirement may be drivenby IEC/ISO/IEEE line harmonic current regulations, as known in the art.

This invention is applicable to conventional electric vehicles (EVs) aswell as grid-charged hybrid electric vehicles (PHEVs). Grid-charged HEVsprovide the option to drive the vehicle for a certain number of miles(i.e., PHEV20, PHEV40, PHEV60). Traditionally, the goal for PHEVs is toprovide a high all-electric-range (AER) capability to lower operatingcost and be able to optimize the operating strategy. In terms of thebuck-boost stages, the charger front-end and interface, it generallymakes little difference if it is designed for an EV or PHEV application.The role of the DC/DC converter is an efficient energy transfer betweentwo or more energy sources, reliable for continuous and peak powerdemands. The integration of the charger unit is the next step towards ahigher power density design with fewer components and therefore higherreliability. As such, embodiments of the invention are applicable tomultiple electric vehicles, including all-electric and hybrid electricvehicles, as examples, designated generally and broadly as “EV”s. SuchEVs may include but are not limited to road vehicles, golf carts,trains, and the like, capable of having power systems that include anelectric component for causing motion of the vehicle.

In conventional implementations many separate units coexist, to includegenerally a separate charger, battery management and control unit thatare interconnected. In an automotive environment with advancedbatteries, communications between the charger and battery is animportant consideration. In such environments seamless integration withbatteries from different battery vendors is also an importantconsideration. The energy management system with integrated charger isadvantageous in that aspect that there is less integration effortrequired and fewer components improve reliability.

Referring now to FIG. 2, configurable multi-port integrated chargerarchitecture, energy storage and management system (ESMS) 100, isgenerically illustrated having four energy ports 102 and three DCelectrical conversion devices or buck-boost converters respectively asmodules 1, 2, and 3 (104, 106, 108). As known in the art, buck-boostconverters 104-108 may be configured to operate in either a buck-mode byflowing electrical energy therethrough in a first direction 110(illustrated with respect to buck-boost converter 104, but equallyapplicable to converters 106 and 108), or a boost mode by flowingelectrical energy in a second direction 112 (illustrated again withrespect to buck-boost converter 104, but equally applicable toconverters 106 and 108). As illustrated, energy ports 102 comprise afirst energy port P1 114 configurable to have a first unit 116 attachedor electrically coupled thereto. Similarly, energy ports 102 comprisefourth, second, and third energy ports P2 118, P3 120, and P4 122 thatare configurable to have respective second unit 124, third unit 126, andfourth unit 128 attached or electrically coupled thereto.

According to the invention the charger is part of the vehicle design andmounted on-board. The integrated on-board charger is capable ofcontinuously adjusting input currents to energy ports 114 and 118-120 asa result of, for instance, varying SOC of devices connected thereto forcharging.

As will be illustrated, ESMS 100 of FIG. 2 may be configured to chargeup to three energy sources (to include low voltage energy batteries,high voltage power batteries, ultracapacitors, as examples) at the sametime or simultaneously. ESMS 100 may have modules therein configured tobe interleaved in order to lower ripple current. ESMS 100 also iscapable of having multiple charging profiles as a function of conditionsthat include SOC and temperature, as examples, for different batterytechnologies and storage device types. ESMS 100 includes a centralizedenergy flow control that is centrally controlled by controller 46 ofFIG. 1, and ESMS 100 is capable of managing a wide range of input andoutput voltages.

ESMS 100 of FIGS. 1 and 2 is configurable in multiple configurations.Each configuration of ESMS 100 may be selectable by contactors. Energyflow is controlled by ESMS control algorithms, implemented in controller46 of hybrid vehicle 10, which can sense a presence of both energystorage devices and charging devices connected to ports 102 and adjust aflow of direction of energy, accordingly. For instance, the controlalgorithms may determine a voltage of each port to which an energystorage device or an electrical charging system (DC or rectified AC, asexamples) is coupled, and operate ESMS 100 accordingly and based on thedetermined voltages, based on a measured frequency, or both (asexamples). And, a benefit for including a rectifier is that even if DCis connected having the wrong polarity, the rectifier providesprotection, even if a single phase rectifier is used or if a DC input isused to two of the 3-phase inputs for a 3-phase rectifier.

The wide input voltage integrated charger allows independent andsimultaneous charging of two or more batteries of any SOC levelrespectively from any input voltage level within the voltage limit ofESMS components. The input voltage can range from typical single phasevoltages (110V/120V), to 208V/240V and up to 400V or even higher (level1 . . . 4). The highest currently specified voltage is 400V for rapid DCcharging, however with proper selection of ESMS components, up to 480Vsingle or 3-phase AC or even 600 V DC can be utilized to provide higherlevel of charging for shorter time duration (i.e., fast charging). Anenergy battery is either connected to first energy port 114 or fourthenergy port 118 and has typically lower nominal voltages than the powerbattery on second energy port 120. Short time energy storage devices,such as ultracapacitors, may be included on first energy port 114.

Generically illustrated ESMS 100 of FIG. 2 may be configured byselective use of switches in order to support a number of chargingarrangements. FIG. 3 illustrates a detailed circuit diagram of amulti-port ESMS according to an embodiment of the invention. Forsimplicity, control electronic components are omitted. Thus, ESMS 200(similar to ESMS 100 of FIGS. 1 and 2) illustrates a first buck-boostmodule 202, a second buck-boost module 204, and a third buck-boostmodule 206. ESMS 200 also illustrates port P1 208 having a relativelylow voltage battery coupled thereto, port P2 210 having a relativelyhigh voltage unit coupled thereto, port P3 212 having a rectified AC orDC voltage coupled thereto, and port P4 214 having a relatively lowvoltage ultracapacitor coupled thereto. Thus, in the exampleillustrated, energy storage devices and an energy charger are coupled toESMS 200 in order to illustrate operation according to oneconfiguration. However, as discussed, ESMS 200 may be configured innumerous arrangements in order to accommodate multiple charger/energystorage arrangements. As such, ESMS 200 includes contactors K3 216, K1218, K2 220, K4 222, and M 224 which may be selectively engaged ordisengaged in order to accomplish configurations for charging, accordingto the illustrations above.

Each of the three buck-boost modules M1 202, M2 204, M3 206 includes anIGBT leg (upper and lower switch) and an inductor. The high voltage DCbus may be buffered by a number of power capacitors. Each buck-boostconverter stage output is equipped with a current sensor, which measuresan inductor current. Voltage limits shown at port P3 212 are originatedby typical single-phase AC outlet voltages in both the US and Europe.However, in applications requiring higher levels of charge power, portP3 can be coupled via charger interface 42 (FIG. 1) to 208V, 240V, or480V 3-phase, or either 400 V DC or up to 600 V DC.

ESMS 200 uses contactors as main bus and individual module switches. Apre-charge circuit is realized using two power resistors (e.g., 120 ohm,100 W, RH-50) and a contactor or FET. An additional contactor (K4 222 inFIG. 3) serves in two cases. One is under a certain SOC condition of abattery at port P1 208, and the second if interleaving of module 1 202and module 3 206 is enabled. FIG. 3 illustrates voltage and currentsense points of ESMS 200 having an integrated charger.

Charging may be using a single battery or a dual battery. Charging in adual battery configuration as shown here allows charging from a wideinput voltage range of batteries with an arbitrary SOC level for bothbatteries. The internal architecture of the multi-port integratedcharger with its software features only allows this. Upon power-up, ESMS200 control recovers the type of energy storage units that are beingused, their energy ratings and limits for charging current and power.From the communication interface to the electric vehicle supplyequipment (EVSE) the ESMS sets limits for input current and eventuallythe type of power source (AC or DC).

Each buck-boost module runs an independent state machine. The states aredisabled/standby, buck mode enabled, boost mode enabled or enabledpermanent conducting upper switch (specific to module 2 204 asillustrated in FIG. 4 as sequence 250). Module state selection occurs atstep 252 and power on self-test occurs at step 254. Input voltage rangeis determined at step 256 and if V_(min) and V_(max) are on the highside 258, then switch K1 218 is closed and module M2 204 is enabled 260,causing module M2 204 to operate in buck mode. If V_(min) and V_(max)are on the low side 262, then switch K1 218 is opened and module M2upper switch is on, causing module M2 204 to be permanently on 264. Atstep 266, module M1 202 is requested and the state of module M2 204(i.e., buck mode at step 202 or permanently on at step 264) is returnedat step 268 for further operation. Part of this sequence is also toforce the contactors into the right state. For charging generallycontactor K3 216 is closed to allow the use of modules M1 202 and M2 204for controlled charging of the port P2 210 energy storage device. Inthis sequence of the charging control the software distinguishes severalcases that might apply and selects the appropriate state of each of thethree buck-boost modules 202-206.

In the start-up sequence and before any contactor is forced to the ONstate and before the modules and switching of the IGBTs are enabled,ESMS 200 control acquires the voltage levels of all used energy sourcesand determines the charger input voltage. This is done in order to avoidany possible uncontrolled current when for example the voltage on thelow side of the buck-boost module is higher than the voltage on the highside. This can be the case for example when the power battery on thehigh side is deeply discharged and the energy storage devices on port P1208 and/or port P4 214 still have a significant amount of energy stored.This is a scenario that is typically avoided by normal operation energymanagement of the vehicle, but it might be possible if the high sideenergy storage device is replaced and not charged up prior toreplacement, or the normal operation energy management was not activefor long time for some reason. The integrated charger control can handleeven very extreme and unusual voltage levels at all four ports 208-214and allows controlled energy management to bring the system back tonormal operation.

In one mode of operation, referring to FIG. 5, a charging current isestablished into the high side energy storage device at port P2 210.This is referred to as the single HV battery charging mode. Module M1202 operates in boost mode, contactors K3 216 and M 224 are closed,while contactors K1 218, K2 220 and K4 222 are open. Depending on thecharger input voltage, module M2 204 is in buck mode (V_(P3)>V_(P2)) orthe upper switch is permanently conducting (V_(P3)<V_(P2)). The chargingcurrent is controlled through module M1 202. Depending on the chargingstrategy, the SOC or the voltage level of the device at port P2 210 thecontrol determines the charging current and the time of operation inthis mode.

As an extension to the mode described before, referring to FIG. 6, thecharger control enables charging of a second energy storage device oneither port P1 208 or port P4 214. This may be referred to as a dualbattery charging mode. In this mode the control ensures that acontrolled current flow is possible before closing the contactors andenabling module M3 206. If the voltage levels are in permissible rangeeither contactor K2 220 or K4 222 are forced into ON state, module M3206 is set into buck mode and determines the charging current and thetime of operation in this mode. An initial power split factor is appliedwhile currents and voltages are constantly monitored to calculate eachindividual SOC. By using a commercial off the shelf (COTS) battery pack,the standardized communication interface of the integrated charger ESMSalso allows to receive voltage and SOC from the system. The integratedcharger ESMS executes the desired charging strategy, which depends onbattery technology, thermal constraints, etc.

SOC of attached energy storage devices is estimated to determine a powersplit from the wide voltage input to the energy storage devices.Individual device SOC is constantly monitored to determine and optimizethe power split factor. This task is responsible for handling extremeSOC levels appropriately. For example, a fully discharged high sidebattery on port P2 210 might operate at voltages that are below thebattery on port P1 208. In this case charging up the high side batteryon port P2 210 is required before a charge power split can be performed.

Referring to FIGS. 5 and 6, energy flow for two configurations ofcharging is illustrated. Referring first to FIG. 5, energy is to flowfrom a charger (not illustrated) positioned on port 3 212, to module 2210, and to module 1 208 operating in boost mode. As such, a DC sourcemay be boosted to a high-voltage output on port 2 210, by ensuring K1218 and K2 220 are open.

In the other example illustrated in FIG. 6, port 1 208 and port 4 214may be charged simultaneously from a DC source (not shown) coupled toport 3 212. Two cases may be considered regarding FIG. 6, as examples.

Case 1: Input voltage at port 3 212 is higher than battery voltage atport 1 208. In this case module 2 204 operates in buck mode and thecurrent ILB in LU is regulated. Contactors K3 216 and K1 218 are closed,while M 224, K2 220 and K4 222 (UPOS) are open.

Case 2: Input voltage at port 3 212 is lower than battery voltage atport 1 208. In this case contactors K3 216, M 224 and K4 222 (UPOS) areclosed, while K1 218 and K2 220 are open. Module 2 204 is inactive (M2is permanently on), module 1 202 operates in boost mode to boost the lowinput voltage up to some higher level. Module 3 206 bucks this voltageback to the set voltage of the energy battery at port 1 208. The currentILC in LW is controlled in a closed loop fashion.

Thus, FIGS. 5 and 6 illustrate different charging scenarios that may beimplemented using ESMS 200 of FIG. 3, illustrating as well the directionof current flow corresponding to the charging arrangement illustrated.However and as stated, ESMS 200 may be used in multiple configurations.Different energy storage types and chargers may be connected to ESMS 200according to embodiments of the invention, as illustrated in FIG. 7 as atable 300. That is, exemplary charging scenarios 1-5 302 includefunctions 304 and the various charger and energy storage devicespositioned at ports 1-4. It is contemplated that, although five chargingscenarios 302 are illustrated, the invention is not so limited and anycharger/storage arrangement is possible.

Referring now to FIG. 8, an exemplary charging arrangement isillustrated that corresponds generally to charging scenario 3 of Table300 of FIG. 7. The configuration illustrated in FIG. 8, configuration400, is illustrated having ESMS 200 with ports P1 208, P2 210, P3 212,and P4 214. Configuration 400 is illustrated in order to showcommunication interface 402 and its operation. An energy battery orultracapacitor 404 is coupled to port P1 208, an ultracapacitor orenergy battery 406 is coupled to port P4 214, and a power battery 408 iscoupled to port P2 210. An AC or DC source 410 is coupled to port P3 212and, as stated above, may be coupled through a charger interface 42 ofFIG. 1. Communication interface 402 is coupled to storage devices404-408, as well as source 410, according to embodiments of theinvention. Communication interface 402 is also illustrated in FIG. 1, incommunication with energy storage 30 (having devices 30-36), controller46, and charger interface 42.

Referring still to FIG. 8, communication interface 402 includes multiplecommunication lines 412, 414, 416, and 418 coupled thereto which enablesensor readings to be carried from respective devices 404-410. That is,communication lines 412-418 are coupled to their respective device inorder to obtain temperature limits and current limits, as examples, thatpertain to devices 404-410, as well as provide realtime feedbackregarding temperature, current, and voltage, of each respective device404-410. Additionally, device parameters such as current state-of-chargeand voltage measurements may be obtained as well from each device404-410.

Thus, referring to FIG. 9, communication interface 402 is configured toreceive multiple inputs from various sources in order to optimizecharging operation, according to the invention. Communication interface402 is coupled to controller 46, which is configured to output twoparameters 420, according to the invention. Two parameters 420 includean overall charging current 422 and a power split 424. That is, based oninformation received from, and regarding the current state of devices404-410, overall charging current 422 and power split 424 are determinedand fed to ESMS 100 in order to optimize regarding of devices 404, 406,and 408, according to embodiments of the invention.

As seen in FIG. 9, communication interface 402 receives a number oftypes of information pertaining to devices 404-410. For instance,communication interface 402 receives limit information 426 that includesbut is not limited to temperature limits of each of the N devices (i.e.,devices 404-410), maximum current pertaining to each, or maximum rate ofcurrent change, as examples. Communication interface 402 also receivesenergy storage device parameters 428 for each of the N devices 404-410as well. Parameters 428 include but are not limited to a state-of-charge(SOC), a minimum voltage, and a maximum voltage, as examples.Communication interface 402 also receives sensor feedback 430 from eachof the N devices 404-410, which includes but is not limited to currentin each device, voltage across each device, and temperature of eachdevice.

Thus, communication interface 402 receives limit information 426, deviceparameter information 428, and realtime sensor information 430 which areprocessed and fed to controller 46 such that overall charging current422 and power split 424 may be determined therein and fed to ESMS 100.ESMS 100 thereby and in turn controls modules M1-M3 therein accordingly.According to one embodiment of the invention, power split 424 is splitbetween high and low voltage sides of ESMS 100 (high voltage sideincludes ports P2 210 and P3 212, while the low voltage side includesport P1 208 and P4 214). That is, referring to FIG. 8 for instance,power split 424 includes a percentage of total power that is directedtoward power battery 408, and the remaining percentage of total powerthat goes to both storage device 404 and storage device 406. Thus, in anembodiment where only one low voltage storage device is coupled to thelow voltage side of ESMS 200, and one high voltage storage device iscoupled to the high voltage side of ESMS 200, then power is splitfractionally to the low and the high voltage storage devices, and thetotal current to both devices is controlled, accordingly.

According to the invention, power regulation to the low and high voltagesides is continuous based on a continuous monitoring of the sensors.According to one embodiment, if one of the low or high voltage storagedevices is fully depleted, then when beginning to charge the low andhigh voltage storage devices, the power split is 100% to the fullydepleted device, after which monitoring as described dictates acontinuous revision of total power and power split, as described.

According to the invention, controller 46 may apply thermal balancing bycontrolling operation of a fan based on feedback, temperature limits,etc. . . . . Thus, referring back to FIG. 1, a fan 432 may be positionedto blow air over one or all of the energy storage devices (32-36) showntherein, which likewise correspond to the energy storage devices 404-408of FIG. 8 or energy storage devices 208, 214, and 210 of FIGS. 5 and 6.Temperature information is usually available from the different energystorage units that can be used to provide a coarse thermally balancedcharging that is achieved by splitting the power flow symmetrically overall modules. In a scenario of at least one Li-Ion battery pack in thesystem, especially if passive balancing is applied, temperatureinformation is usually available to be used by the charging control. Athermal model can be used if the sensor distribution is coarse or thebattery technology allows easy prediction of the temperaturedistribution inside the pack. Thus, for thermal balancing the controlobjective is to balance battery pack temperature distribution and, inaddition to controlling total current 422 at port P3, and power split424 between units, fan operation can be controlled as well using fanspeed control, thermal modeling, and the like, in order to optimizethermal performance of the energy storage devices.

According to the invention, power may be maximized to the high voltageside (i.e., the power battery). The objective of this charging strategyis to bring the DC link voltage up rapidly and utilize fully theavailable power to charge the power battery. This might be desired ifthere are shorter discharge and charging cycles desired or possible.Therefore a more frequent recharging is performed by the highperformance power battery, both the DC link voltage is kept relativelyhigh and boosting energy from the second battery is avoided to improveefficiency. Thus, in this scenario the control objective is to maximizea state-of-charge at port P2 on the high voltage side and in the powerbattery in the shortest amount of time, in addition to controlling totalcurrent 422 at port P3, and power split 424 between units.

According to the invention, depending on the dual battery configuration(e.g., power battery and energy battery of similar capacity), it may bedesired to keep the energy balanced within the dual batteryconfiguration during charging. The state-of-charge levels of bothbatteries that are available to the integrated charger energy managementare controlled to be on equal levels within an acceptable error. Thus,in this scenario the control objective is to maintain the state ofcharge (SOC) at both ports P1 and P2 at a similar level, and further torise their respective SOC with a similar slope, by controlling totalcurrent 422 at port P3, and power split 424 between units.

According to the invention, by using Li-Ion battery technology, wherecell groups need to be individually balanced, due to aging temperatureeffects or discharge rates, the individual cell groups might beimbalanced significantly. An optimal pack balancing strategy includeskeeping minimum and maximum cell voltages within a limit. A subsequentcontrol uses available energy to charge a lesser constrained battery ofa different technology. However, an imbalanced Li-Ion battery packusually requires long charging times since active or passive balancingis time consuming while the charging current has to be reducedsignificantly and over a long period. Thus, in this scenario the controlobjective includes minimizing a voltage gap between maximum and minimumcell voltages of both batteries, such as at ports P1 and P2, bycontrolling total current 422 at port P3, and power split 424 betweenunits.

According to the invention, minimizing losses and therefore maximizingefficiency of the overall system is a goal, and many parameters need tobe considered during the design of the DC-to-DC converter and the boostinductors. Once the multi-port buck-boost converter design is finalized,loss optimized control can be achieved for example through operating theconverter predominately in a range of high efficiency. This is in manycases around rated power rather at light load, where efficiency usuallydrops. Also if a small discharge cycle can be assumed, for example ina<40 mile daily commute mode is selected, the use of the boost can belimited to the absolute necessary during driving operation. Thecapability of the battery providing power is based on the history ofcharge and discharge cycles. A high C-rate operation strategy has animpact on the internal resistance and causes faster aging. With that anefficiency optimized operation strategy is linked to a lifetimeoptimized strategy to some degree. Thus, in this scenario the controlobjective is to operate at maximum of the efficiency curves, obtained bycontrolling total current 422 at port P3, and power split 424 betweenunits.

Thus, numerous control schemes and optimization scenarios are included,which may be optimized according to embodiments of the invention.Examples given include but are not limited to thermal balancing,maximizing power to the high voltage side (power battery), balancingstate-of-charge levels, optimal pack balancing, and loss minimizedcontrol.

Source 410 of FIG. 8 includes an AC or a DC source 410 that iscoupleable to ESMS 200 during periods when vehicle 10 is parked (such asat a charging station, at home in a garage, or during work, asexamples). However, the invention is not necessarily limited to chargingwhen vehicle 10 is stationary. That is, according to the invention, anauxiliary power unit (APU) may be included that is positioned on vehicle10 that enables energy storage system re-charge as well as providingpower for vehicle operation. Referring to FIG. 10, vehicle 10 in thisembodiment includes an APU 500 in lieu of the energy battery 404 of FIG.8. Thus, consistent with vehicle 10 of FIG. 1, vehicle 10 may include inaddition to heat engine 12, an APU that provides auxiliary power toelectric motor 26 via ESMS 200 (also labeled as ESMS 100 in FIG. 1). APU500 may include an internal combustion engine (ICE), a permanent magnetgenerator (PMG), or a fuel cell (FC), as examples. That is, in lieu of alow voltage/high energy, energy storage system such as LV supply 32 ofFIG. 1, APU may provide electrical power to system 10 via ESMS 200 toprovide power for vehicle cruising, or to provide power for re-charge ofother energy storage units 406, 408. For instance, in one mode ofoperation, heat engine 12 may provide power to electric motor 26 toprovide power for vehicle operation, while at the same time, APU 500 canprovide re-charging energy to energy storage units 406, 408. In suchfashion, energy use can be optimized by selectively providing power fromheat engine 12 and re-charging other storage units for peak efficiency.The APU 500 provides additional flexibility of operation and enablesindependent or simultaneous charging of both batteries 406, 408, andextends the integrated charging control. Charging is no longer limitedto stationary charging.

In another embodiment of the invention, referring to FIG. 11, vehicle 10includes APU 500 positioned thereon that is switchably coupleable toport P3 212. That is, APU 500 is an auxiliary unit positioned on vehicle10 but, instead of being coupled to ESMS 200 via port 1 208 as in FIG.10, APU 500 is coupled to port P3 212 via a switching device 502. Thus,according to this invention, instead of having port P1 208 dedicated toproviding power from APU 500, port P1 208 may be dedicated to couplingan energy battery or an ultracapacitor 404 as in previous illustrations,and port P3 212 may be used for providing charging from a stationarysource 410 as well as providing auxiliary power during vehicleoperation. That is, by coupling APU 500 through charging port P3 212,additional flexibility of operation is provided because energy can bedrawn for vehicle operation via heat engine 12, energy batteries 404,406, power battery 408, as well as from APU 500. When stationary,switching device 502 may be switched to enable re-charge from astationary source 410.

Thus, overall charging control can be extended beyond a stationary casewhere AC/DC power is provided from the grid via stationary supply 410.Charging control strategies can be centralized, which allowsinteroperability of different battery chemistries on one electricvehicle system. That is, because of the sensor feedback, limitinformation for specific battery types and energy storage types, andbecause of the ability to obtain and use device parameter information inrealtime during vehicle operation, system flexibility is improved andefficiency is optimized, which is all provided through a singlecentralized energy storage and managements system.

A technical contribution for the disclosed apparatus is that it providesfor a controller implemented technique of charging energy storagedevices of an electric vehicle using a multiport energy managementsystem, based on system feedback.

One skilled in the art will appreciate that embodiments of the inventionmay be interfaced to and controlled by a computer readable storagemedium having stored thereon a computer program. The computer readablestorage medium includes a plurality of components such as one or more ofelectronic components, hardware components, and/or computer softwarecomponents. These components may include one or more computer readablestorage media that generally stores instructions such as software,firmware and/or assembly language for performing one or more portions ofone or more implementations or embodiments of a sequence. These computerreadable storage media are generally non-transitory and/or tangible.Examples of such a computer readable storage medium include a recordabledata storage medium of a computer and/or storage device. The computerreadable storage media may employ, for example, one or more of amagnetic, electrical, optical, biological, and/or atomic data storagemedium. Further, such media may take the form of, for example, floppydisks, magnetic tapes, CD-ROMs, DVD-ROMs, hard disk drives, and/orelectronic memory. Other forms of non-transitory and/or tangiblecomputer readable storage media not list may be employed withembodiments of the invention.

A number of such components can be combined or divided in animplementation of a system. Further, such components may include a setand/or series of computer instructions written in or implemented withany of a number of programming languages, as will be appreciated bythose skilled in the art. In addition, other forms of computer readablemedia such as a carrier wave may be employed to embody a computer datasignal representing a sequence of instructions that when executed by oneor more computers causes the one or more computers to perform one ormore portions of one or more implementations or embodiments of asequence.

According to one embodiment of the invention, an electric vehicleincludes a controller configured to receive sensor feedback from a highvoltage storage device and from a low voltage storage device, comparethe sensor feedback to operating limits of the respective high and lowvoltage storage device, determine, based on the comparison a totalcharging current to the high voltage storage device and to the lowvoltage storage device and a power split factor of the total chargingcurrent to the high voltage device and to the low voltage device, andregulate the total power to the low voltage storage device and the highvoltage storage device based on the determination.

In accordance with another embodiment of the invention, a method ofmanaging an energy storage system for an electric vehicle includesreceiving sensor feedback from a high voltage energy storage device ofthe electric vehicle, comparing the sensor feedback from the highvoltage energy storage device to an operating limit specific to the highvoltage energy storage device, receiving sensor feedback from a lowvoltage energy storage device of the electrical vehicle, comparing thesensor feedback from the low voltage energy storage device to anoperating limit specific to the low voltage energy storage device,determining, based on the comparison from the high voltage device andfrom the low voltage device a total charging current to the high voltagestorage device and to the low voltage storage device and a power splitfactor of the total charging current to the high voltage device and tothe low voltage device, and regulating the total power to the lowvoltage storage device and the high voltage storage device based on thedetermination.

In accordance with yet another embodiment of the invention, a computerreadable storage medium coupled to an energy storage and managementsystem (ESMS) of an electric vehicle (EV) and having stored thereon acomputer program comprising instructions which when executed by acomputer cause the computer to receive sensor feedback from a highvoltage energy storage device of the EV and from a low voltage energystorage device of the EV, compare the sensor feedback to operatinglimits of the respective energy storage devices, determine, based on thecomparison a total charging current to the energy storage devices and apower split factor of the total charging current between the highvoltage device and the low voltage device, and regulate the total powerto the energy storage devices based on the determination.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. An energy storage and management system (ESMS) comprising: a plurality of energy ports comprising a first energy port, a second energy port, a third energy port and a fourth energy port, each of the plurality of energy ports being connectable to a charging device or an energy storage device; a plurality of DC electrical conversion devices selectively connected to the plurality of energy ports and configured to step up and to step down a DC voltage, the plurality of DC electrical conversion devices comprising a first DC electrical conversion device, a second DC electrical conversion device, and a third DC electrical conversion device; and a plurality of contactors each selectively engaged or disengaged to control a charging power provided to one or more of the plurality of energy ports, so as to provide a controlled charging of one or more energy storage devices connected to the respective energy ports.
 2. The ESMS of claim 1 wherein the first DC electrical conversion device, second DC electrical conversion device, and third DC electrical conversion device comprise a first buck-boost module, a second buck-boost module, and a third buck-boost module, with each of the first, second and third buck-boost modules operable in a standby mode, a buck mode, a boost mode, and a permanent conducting mode.
 3. The ESMS of claim 2 further comprising a controller configured to selectively control operation of the first, second, and third buck-boost modules and selectively control operation of the plurality of contactors.
 4. The ESMS of claim 3 wherein the first energy port comprises a high voltage port couplable to a boosted voltage side of each of the buck-boost modules; wherein the second eneregy port is a low voltage port couplable to a bucked voltage side of each of the buck-boost modules; and wherein at least one of the third and fourth energy ports is coupleable to a charging device.
 5. The ESMS of claim 4 wherein the controller is configured to: receive sensor feedback from a high voltage storage device coupled to the first energy port and from a low voltage storage device connected to the second energy port; compare the sensor feedback to operating limits of the respective high and low voltage storage device; determine, based on the comparison: a total charging current to the high voltage storage device and to the low voltage storage device; and a power split factor of the total charging current to the high voltage storage device and to the low voltage storage device; and regulate the total power to the low voltage storage device and the high voltage storage device based on the determination.
 6. The ESMS of claim 5 wherein the controller is configured to cause each of the plurality of contactors to be selectively engaged or disengaged based on the determined total charging current and power split factor.
 7. The ESMS of claim 5 wherein the controller is configured to: determine a voltage of each of the plurality of energy ports; determine the power split factor based on the determined voltages of each respective energy port.
 8. The ESMS of claim 5 wherein the controller is configured to: continuously receive the sensor feedback from the high and from the low voltage storage devices; compare the continuously received sensor feedback to the operating limits of the respective high and low voltage storage devices; revise the determined total charging current and the power split factor; and regulate power to the low voltage storage device and the high voltage storage device based on the revised determination.
 9. The ESMS of claim 5 wherein the controller is configured to determine the power split factor such that, when regulating power to the high voltage and to the low voltage energy storage devices, power is directed to only one of the high and low voltage energy storage devices.
 10. The ESMS of claim 5 wherein the operating limits of the respective high and low voltage storage devices are comprised of at least one of an electrical current limit and a maximum temperature corresponding to each of the respective high and low voltage storage devices.
 11. The ESMS of claim 3 wherein the controller is configured to: receive sensor feedback from each energy storage device coupled to the plurality of energy ports; receive sensor feedback from each charging device coupled to the plurality of energy ports; compare the sensor feedback from each energy storage device to the sensor feedback from each charging device; and control operation of the first, second, and third buck-boost modules and of the plurality of contactors based on the comparison.
 12. A vehicle propulsion system comprising: an electric motor; an energy storage system configured to provide power to the electric motor, the energy storage system comprising a plurality of energy storage devices; a charger interface coupleable to a charging device to receive charging power therefrom for recharging the energy storage system; and an energy storage and management system (ESMS) coupled to the energy storage system and the charger interface to selectively transfer the charging power from the charger interface to the energy storage system; wherein the ESMS comprises: a plurality of energy ports each connectable to a respective one of the plurality of energy storage devices or the charger interface; a plurality of buck-boost converters in operable communication with the plurality of energy ports and configured to step up and to step down a DC voltage; and a plurality of contactors each selectively engaged or disengaged to control a charging power provided to one or more of the plurality of energy ports, so as to provide a controlled charging of one or more energy storage devices connected to the respective energy ports.
 13. The vehicle propulsion system of claim 12 wherein the plurality of energy storage system comprises a low voltage energy storage device, a high voltage energy storage device, and an ultracapacitor.
 14. The vehicle propulsion system of claim 13 wherein the plurality of energy ports comprises a first energy port, a second energy port, a third energy port and a fourth energy port, and wherein the plurality of buck-boost converters comprise a first buck-boost converter, a second buck-boost converter, and a third buck-boost converter; wherein the high voltage storage device is coupled to the first energy port, the low voltage storage device is coupled to the second energy port, the charger interface is coupled to the third energy port, and the ultracapacitor is coupled to the fourth energy port.
 15. The vehicle propulsion system of claim 14 further comprising a controller configured to selectively control operation of the first, second, and third buck-boost modules and selectively control operation of the plurality of contactors.
 16. The vehicle propulsion system of claim 15 wherein the controller is configured to: receive sensor feedback from the high voltage storage device coupled to the first energy port and from a low voltage storage device connected to the second energy port; compare the sensor feedback to operating limits of the respective high and low voltage storage devices, the operating limits comprised of at least one of an electrical current limit and a maximum temperature corresponding to each of the respective high and low voltage storage devices; determine, based on the comparison: a total charging current to the high voltage storage device and to the low voltage storage device; and a power split factor of the total charging current to the high voltage storage device and to the low voltage storage device; and regulate the total power to the low voltage storage device and the high voltage storage device based on the determination.
 17. The vehicle propulsion system of claim 16 wherein the controller is configured to cause each of the plurality of contactors to be selectively engaged or disengaged based on the determined total charging current and power split factor.
 18. The vehicle propulsion system of claim 16 wherein the controller is configured to determine the power split factor such that, when regulating power to the high voltage and to the low voltage energy storage devices, power is directed to only one of the high and low voltage energy storage devices.
 19. The vehicle propulsion system of claim 15 wherein the controller is configured to: receive sensor feedback from each energy storage device coupled to the plurality of energy ports; receive sensor feedback from each charging device coupled to the plurality of energy ports; compare the sensor feedback from each energy storage device to the sensor feedback from each charging device; and control operation of the first, second, and third buck-boost modules and of the plurality of contactors based on the comparison. 